1. Field of the Invention
The invention relates to a method and apparatuses for characterizing groundwater measuring sites by differentiating between groundwater and static water by determining groundwater parameters at measuring sites and can be used for the on-site determination of the optimum sampling time, for the determination of the pumping-out times optimum for-investigations of the representative condition and for monitoring groundwater measuring sites for defects. The invention can be used, in particular, within the scope of investigating the condition of groundwater.
The protection of groundwater for producing drinking water, as well as the checking of suspected abandoned polluted areas, the investigation of abandoned polluted areas and the clean-up of damage make it necessary to obtain a constantly increasing number of groundwater samples. Groundwater observation pipes and groundwater measuring sites were and are being set up in order to sample the groundwater. At the same time, the analytical methods for determining the components of the water were refined and the spectrum of individual materials detectable was expanded. Both led to new demands for the quality of groundwater samples. The high requirements of analysis and the financial expense involved in obtaining groundwater samples likewise require a careful depth-oriented and representative sampling. A prerequisite for this is the correct selection of measurement site type, sampling techniques and sampling technology. Moreover, for ensuring that a groundwater sample is representative, it is necessary to know the optimum pumping-out time. If a sample, because the pumping-out time selected has been too short, contains larger amounts of static water from the groundwater observation pipe, the evaluation of the results of analysis can lead to wrong conclusions. On the other hand, excessively long pumping-down times can attract water bodies from other levels, which is also undesirable. The correct determination of pumping-down times for groundwater observation pipes is a problem, which heretofore has not been solved completely.
Before any sample is taken, the groundwater observation pipe, which is to be sampled, must be pumped out until the pumped water corresponds to that of the surrounding groundwater and is no longer influenced by the measuring site. In this connection, it is known that the pumping out should be continued until the electrical conductivity, the temperature and the pH reach constant values. At the same time, it is known that the electrical conductivity is only an orienting parameter. Further known methods, such as the repeated exchange of the contents of the pipe, are rules of thumb. In summarizing, it can be surmised that the constancy of the electrical conductivity is the generally employed criterion at the present time for determining the time for taking a representative sample, although only little is known about the processes, which cause the decrease in electrical conductivity in a ground water observation pipe.
It is a disadvantage of this method that, although the constancy must be regarded as a necessary conditions for a subsequent sampling, it is not a sufficient condition, since the electrical conductivity can reach a plateau value even before the time, at which a representative sample can be taken. This occurs, for example, when the ground water observation pipe has already been sampled days or weeks before the sample is taken. On the other hand, the radon activity concentration can be taken as a reliable criterion, even if only a few days have elapsed between the two samplings. Moreover, the relative change between the initial value (static water) and the final value (groundwater) generally is several times smaller for conductivity than for the radon activity concentration, which makes it easier to establish the optimum time for taking representative samples when the radioactivity concentration is used.
2. Description of the Related Art
Such a method for determining the optimum pumping out times of groundwater observation pipes for establishing an optimum time for sampling is known from DE 3911366 C2. For this method, the conductivity of the water is monitored and representative sampling is initiated when the conductivity is constant
Furthermore, the DE 42 17 263 A1 discloses a method, with which gaseous components are also monitored for the sampling. However, this method is concerned not with using gas for establishing the sampling time but with a method of gas sampling, which is similar to the groundwater sampling.
Finally, from the literature references, Health Physics, vol. 53 (1987), pages 181-186 and Radioisotopes, vol. 30 (1981), pages 649-654, methods are known for measuring radon in air (unsaturated zone, ground air) by the LSC method. For this method, radon-containing air is blown with an inlet tube into stationary water in order to dissolve in the water. It can then be extracted from the water once again with an LSC cocktail and measured.
The invention is based on the objective of providing a method for characterizing groundwater measuring sites by differentiating between groundwater and static water and for determining the optimum pumping-out times of the groundwater observation pipes, which method is optimum for investigating the condition and permits the optimum pumping-out time to be determined reliably and reproducibly with high accuracy at a cost that is justifiable and ensures a reliable determination of the ratio of groundwater to static water in a groundwater sample, as well as the localization of defects.
Pursuant to the invention, this objective is accomplished by the distinguishing features in the characterizing part in claim 1. Appropriate developments of the invention are contained in the dependent claims.
A special advantage of the invention consists therein that the optimum pumping-out times and the optimum times for the sampling are determined with very high accuracy and reproducibility, in that water samples are taken at defined, consecutive times during the pumping-out process, the radon activity concentration of the samples taken is measured and the attainment of a radon activity concentration, which remains essentially constant, signals the optimum time for representative sampling.
A further advantage of the invention lies therein that the groundwater measuring site parameters can be determined without a delay of time, in that the radon activity concentration and/or the total activity concentration are determined and evaluated spectrometrically and/or by diffusion into an air volume or degassing by subsequent measurement in situ directly from the groundwater that is to be investigated.